The present invention relates to an artificial ventilation apparatus including a carbon dioxide concentration sensor.
An artificial ventilation apparatus is equipped with functions of detecting a non- or hypo-ventilated state of the patient due to malfunction of a ventilator or an abnormality of a respiratory circuit, and generating an alarm. Particularly, it is said that End-tidal CO2 (EtCO2) monitoring is useful because it is possible to check that the patient actually performs gas exchange.
An EtCO2 measuring mechanism mounted on an artificial ventilation apparatus or on a patient monitoring apparatus other than an artificial ventilation apparatus is configured as shown in FIG. 4.
The apparatus shown in FIG. 4 is a related-art artificial ventilation apparatus, and configured in the following manner. A ventilator 80 is connected to the respiratory system of the patient A through an inspiratory valve 82 which is a one-way valve, an infection prevention filter 86, a heating and humidifying device 87, a water trap 88, and a respiratory circuit 81. The respiratory system of the patient A is connected to an exhaust portion 91 of the ventilator 80 through the respiratory circuit 81, a water trap 89, an infection prevention filter 90, and an expiratory valve 83 which is a one-way valve. A respiratory gas is sent from the ventilator 80 to the patient through the inspiratory valve 82, and the expiratory gas of the patient is discharged from an exhaust port 91A through the expiratory valve 83 and the exhaust port 91.
In the related-art artificial ventilation apparatus, a carbon dioxide concentration sensor 84 is disposed at a position near the mouth of the patient A, to measure the EtCO2 of the patient A, thereby monitoring the situation of the gas exchange of the patient A. The devices and appliances which include the carbon dioxide concentration sensor 84, and which exist between the patient A and the ventilator 80, i.e., the infection prevention filters 86, 90, the heating and humidifying device 87, the water traps 88, 89, and the respiratory circuit 81 are configured so as to be easily attached and detached, in order to enable replacement, sterilization, or replacement for every patient (for example, see FIG. 1 of JP-UM-B-6-20535).
The ventilator 80 includes a power supply portion 85 which supplies an electric power to various portions of the ventilator 80. The power supply portion 85 performs a necessary power supply also on the carbon dioxide concentration sensor 84. However, some of simple ventilators which are operated manually or by an additional pressure source or the like do not include a power supply portion.
There is a related-art artificial ventilation apparatus which detects the carbon dioxide concentration by using the side stream method, in which the volume of carbon dioxide is calculated by a carbon dioxide concentration detector that is connected through a sampling tube to the middle of an expiratory circuit located upstream of an expiratory circuit, and a flow rate meter that is connected to an inspiratory circuit (see JP-A-2002-11100).
In the related-art apparatus shown in FIG. 4 or JP-UM-B-6-20535, as described above, many portions which can be easily attached and detached exist between the ventilator 80 and the patient A, and hence the probability that a connecting portion is disconnected is correspondingly increased. Particularly, there is a possibility that disconnection of an inspiratory circuit portion may seriously affect the patient. Therefore, there is a very cumbersome problem in that it is necessary to check that the carbon dioxide concentration sensor 84 and the like are surly attached, so that a ventilation failure in the patient due to disconnection of a connecting portion, malfunction of the alarm due to disconnection of the sensor, a ventilation failure in the patient due to the malfunction, or the like does not occur.
The respiratory gas is humidified by the heating and humidifying device 87, and the carbon dioxide concentration sensor 84 is disposed at the position near the mouth of the patient A. Therefore, dew condensation easily occurs in circuits in the vicinity of the carbon dioxide concentration sensor 84. When dew condensation once occurs, normal detection of the carbon dioxide concentration by the carbon dioxide concentration sensor 84 is hardly conducted. This may cause malfunction of an alarm or the like.
In the case where the patient performs spontaneous respiration, when the expiratory circuit (for example, the connecting portion of the infection prevention filter 90) of the respiratory circuit 81 is disconnected, or when the inspiratory circuit (for example, the connecting portion of the infection prevention filter 86) of the respiratory circuit 81 is disconnected, the respiratory gas is not sent to the patient. However, the carbon dioxide concentration sensor 84 detects carbon dioxide produced by spontaneous respiration of the patient, and hence the disconnection cannot be detected by the carbon dioxide concentration sensor 84. In the case where the patient does not perform spontaneous respiration, when the inspiratory circuit is disconnected, the respiratory gas cannot be supplied, and hence the detection value of the carbon dioxide concentration sensor 84 becomes abnormal, so that the abnormal state can be detected. By contrast, when the expiratory circuit is disconnected, a case where the disconnection cannot be detected may be possible depending on the portion where the disconnection occurs. If the disconnected portion is near the expiratory valve 83, namely, the pipe resistance of the expiratory circuit is large. This allows the respiratory gas to be sent to the patient, and carbon dioxide is detected by the carbon dioxide concentration sensor 84. Therefore, there is a possibility that the disconnection cannot be detected.
In the specification, the term “disconnection can be detected” means that, when disconnection occurs, the carbon dioxide concentration detected by the carbon dioxide concentration sensor becomes an abnormal state, and not always means that the disconnected portion is identified. The term “disconnection cannot be detected” means that the carbon dioxide concentration detected by the carbon dioxide concentration sensor does not become abnormal.
In the related-art apparatus shown in FIG. 4, the single power supply portion 85 supplies an electric power to the ventilator 80 and the carbon dioxide concentration sensor 84. When the power supply portion 85 does not function, therefore, the ventilator 80 does not operate, and at the same time also the carbon dioxide concentration sensor 84 does not work, with the result that an alarm is not generated, and the abnormality cannot be known. Usually, a simple ventilator which does not include such a power supply portion fails to have a function of monitoring the carbon dioxide concentration.
In the related-art apparatus disclosed in JP-A-2002-11100, the carbon dioxide concentration detector is connected to the side of the expiratory circuit, but the sampling tube for the expiratory gas is connected to the upstream side of the expiratory valve. The sampling tube and the carbon dioxide concentration detector must be configured so as to be easily attached and detached, in order to enable replacement, sterilization, or replacement for every patient. Therefore, also the apparatus has a very cumbersome problem in that it is necessary to check that the carbon dioxide concentration detector and the like are surly attached, so that a ventilation failure in the patient due to disconnection of a connecting portion, malfunction of the alarm due to disconnection of the sensor, a ventilation failure in the patient due to the malfunction, or the like does not occur.